Trio of weather problems denying region needed rain, forecasters say

Jun 13, 2011

The following article was published in the Palm Beach Post on June 13, 2011:

Trio of Weather Problems Denying Region Needed Rain, forecasters say

By Alexandra Seltzer

Where’s the rain?

That’s the question being asked by frustrated Palm Beach County residents these days.

West Palm Beach is drying up to the point it’s buying water from the county. Brush fires are igniting daily up and down the coast. The toughest watering restrictions in years are threatening the sanctity of well-manicured South Florida lawns. And even though some showers were predicted, the weekend brought little, if any, rain.

To be sure, the region’s nearly 6 million residents are suffering through an unprecedented, “exceptional” drought, according to weather officials and water managers.

But why?

The officials point to three weather phenomena as the main culprits – the North Atlantic Oscillation, La Niña and the Bermuda High – plus a bit of bad timing.

“October was the driest on record. That was not a good start,” said Geoff Shaunessey, chief meteorologist for the South Florida Water Management District. “The oscillation just complicated things.”

The first two factors not only kept out what little rain would have come during the dry season, but also ushered in weather cold enough to freeze crops in the Glades. Just as La Niña began to weaken, the Bermuda High moved in to block the area’s typical afternoon thunderstorms.

Even those limited showers would be welcome. National Weather Service forecasters say the region needs something on the level of 2008’s Tropical Storm Faye to bounce back from the drought. Faye storm dumped as much as 15 inches of rain in places, and 8 to 10 inches over much of Palm Beach County.

That may take a while. Forecasters are saying the chance of daily showers and thunderstorms is 20 percent to 30 percent this week.

“It won’t bring us back to normal,” said Robert Molleda, National Weather Service warning coordination meteorologist, of any rains the area might get this week. “But it’s something.”

Problems began last fall

The path to the drought – declared D4, or exceptional, by a group of state and federal meteorologists – began as far back as October with the start of the dry season, forecasters say.

The North Atlantic Oscillation is a climatic condition that has two phases, positive and negative. A positive phase brings wetter conditions to the eastern United States, and a negative phase brings drier-than-usual conditions. The oscillation went into its negative phase near Greenland in mid-fall and soon began producing the cold weather and freezes that the county endured through January.

The result: Only 6.58 inches of rainfall fell from October through January, compared with the average 17.87 inches.

Barry Baxter, weather service meteorologist in Miami, said the oscillation was producing “dry” cold fronts while keeping the jet stream to the north.

“It’s just acting like a blocker in that it is stopping any kind of front that would produce rain,” state meteorologist Amy Godsey added.

Godsey and other state weather officials agree, however, that La Niña is mostly to blame for the lack of rain .

The weather phenomenon is known to produce conditions drier and cooler than normal, and this year it has been one of the five strongest on record, officials said.

Bolstered by the oscillation, it was a big contributor to the region’s record-low rainfall from October through February (7.47 inches). In addition, La Niña, even as it grows weaker, has been weakening the subtropical jet stream that typically steers low-pressure systems providing some rainfall toward South Florida.

“Without that energy, we get weaker systems that don’t produce rain,” the water management district’s Shaunessey said.

Forecasters expected that when La Niña finally began losing its power, which would allow for more rain, the Bermuda High would make its way to South Florida. The Bermuda High is an area of high pressure that hovers over the island and that sometimes extends itself westward and creates weather problems for the Atlantic Coast. It has sat over Florida for at least a few weeks.

Godsey said the high is especially disturbing now because it is “abnormally strong.” The high pressure is “suppressing sea-breeze activity,” and Godsey said that’s a problem because South Florida usually depends on sea-breeze activity to get rain and moisture to develop.

South Florida is receiving dry northeasterly winds from Bermuda because of the high.

“It’s a dry little island for good reason,” Shaunessey said.

“The pattern in the first week of June has been more like what you see in April,” Shaunessey said. “You don’t want to see an April pattern in June. “

Consistent rains needed

Godsey said the latest forecasts show that some welcome wet relief is on the way, because models forecast La Niña and the Bermuda High to weaken.

And none too soon. June is known to be the year’s rainiest month, typically bringing six “big rain days” that South Florida depends on, Shaunessey said.

“We need those pounding, big rain days to maintain water supply and improve long-term conditions,” he said.

More than that, state weather officials agree that sea-breeze raindrops just won’t bring the amount of wet weather the region needs.

Palm Beach International Airport has recorded a mere 0.72 inches of rain this month. Usually, PBIA records almost 8 inches of rainfall in June. But for conditions to improve, weather service meteorologists say the county needs about 12 inches above normal – 20 inches – for the month.

“We’re not expecting to eliminate the drought in one month,” said Molleda, the weather service meteorologist. “It would have to be something unusual.”

From January through Sunday, rainfall at the airport was 14.81 inches below normal. South Florida usually receives the most rain between Memorial Day and the Fourth of July.

“In South Florida we live and die by our own rainfall,” Shaunessey said. “We live and die by the rain that falls directly in our district. That’s a blessing and a curse at the same time.”

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